1. Field of the Invention
This invention relates to a motor vehicle horn blowing switch arrangement, on the steering wheel of which vehicle an inflatable occupant restraint system is mounted.
2. Description of the Prior Art
Horn blowing switch arrangements have been proposed in the prior art for vehicles on the steering wheels of which inflatable occupant restraint systems are mounted. U.S. Pat. No. 3,819,205 discloses a so-called modular occupant restraint system in which an inflator, an inflatable cushion or air bag, and a generally rectangular cover or container for the cushion are all assembled on a support plate which, in turn, is mounted to the steering wheel. Extending from each upper corner of the cover is a portion which is provided with a horn blowing switch of the finger deflectable or pressure actuated push button type. A problem with this arrangement is that when access to the switches for repair or replacement is necessary, the cover must be disassembled from the support plate before the switches are exposed.
U.S. Pat. No. 4,148,503 discloses a similar occupant restraint system wherein the horn blowing switch comprises four horn blowing push buttons installed on the four spoke portions, respectively, of the steering wheel externally of the cover for the occupant restraint system.
U.S. Pat. No. 4,325,568 discloses a similar modular occupant restraint system assembled to a support plate having laterally extending pairs of arms and a horn blowing switch which is releasably pivotally connected to one arm and releasably secured to the other arm, with the switch being exposed for repair or replacement without disassembly of any of the components of the system. Spoke extensions of the steering wheel are horn buttons which actuate the switch.
U.S. Pat. No. 4,785,144 discloses a modular occupant restraint system in which a horn blowing switch is actuated when the module cover is depressed. The horn blowing switch includes a support that is mounted within the hub portion of the steering wheel and is provided with a plurality of bolts each of which supports a sleeve member. The bolts thread into the inflatable restraint module. Springs between the support and restraint module space the sleeves from the support. Depression of the module engages the sleeve members with the support to complete the circuit to blow the horn. Access to the switch for repair and replacement requires disassembly of the module. Another problem is that the avoidance of the effects of vibration on the module, transmitted from the steering wheel, requires the use of relatively strong springs. This, in turn, requires a relatively strong pressing force on the module in order to operate the horn.
U.S. Pat. No. 4,002,306 discloses an occupant restraint system having a plurality of membrane switches of plane rectangular shape applied to and arranged on the upper surface of the upper wall of a soft synthetic resin pad of a steering wheel, except for a break-open area defined by a thinned breaking portion in H-like shape, with the manner of attachment of the switches to the pad not being specified. It is contemplated that the membrane switches may be arranged on the rear surface of the upper wall of the pad. There are several disadvantages with these arrangements. The soft synthetic resin pad is rather deficient in respect of providing a suitable reaction surface for horn switch actuation. Servicing or replacement of the switches necessarily involves exposing internal components of the air bag module assembly, particularly in the case of applying the switches to the rear of the pad, and probably also when the switches are applied to the upper surface thereof because of the probability of damaging the pad when attempting to remove the switches for repair or replacement. Additionally, the arrangement of the lead wires from the membrane switches along side wall portions of the pad to a horn actuating circuit within the vehicle, as illustrated and described, leaves much to be desired in an occupant restraint system that is expected to be operable over the life of the vehicle which may be ten (10) years or more.
All of the horn blowing switch arrangements provided for use with inflatable occupant restraint systems mounted on the steering wheel of vehicles disclosed in the foregoing U.S. patents are disadvantageous in one respect or another. U.S. Pat. Nos. 3,819,205, 4,148,503, and 4,325,568 involve the pressing of buttons that are located adjacent the rim of the steering wheel While U.S. Pat. No. 4,785,144 provides actuation of the horn blowing switch when the restraint system module is given a strong push, the structure is complicated and costly to manufacture, and moreover, does not allow access to the switch for repair and replacement without disassembly of the restraint module In U.S. Pat. No. 5,002,306 actuation of the horn blowing switches requires weak pushing only of the pad but inherently appears to be subject to a number of disadvantages including difficulty when attempting repair or replacement of the switches tending to result in damage to the pad or exposure of the internal components of the restraint module, or interference with the use of a decorative cover for the pad.
Thus there is a need for improvement in horn blowing switch arrangements for vehicles on the steering wheels of which inflatable occupant restraint systems are mounted. The present invention was devised to fill the gap that has existed in the art in this respect.